School of Physics Lecture Demonstration Manual

Oc-1 Measurement of the Wavelength of Light Using a Ruler

Published: Wednesday 15 March 2006 - Updated: Monday 28 March 2011


To obtain a measurement of the wavelength of light using diffraction markings on a ruler.



Click on pictures to enlarge.

Measuring Lamda equation

wavelength Measurement with ruler Diagram


The experimental setup shown above uses the half mm markings as a reflection grating. By measurement of the distance to the image and the distance between interference maxima simple calculation yields lambda.

Taking O as the origin (the mid point between the zeroth order specularly reflected beam and the direct beam) the condition for constructive interference is given by the equation above.

Safety notes

Electrical safety 

Laser safety 


top of page